The present invention relates to an imaging device and a manufacturing method thereof.
An imaging device includes effective pixels and optical black (OB) pixels in a pixel region. The effective pixel is a pixel that receives incident light and obtains an electrical charge by a photoelectric effect. The OB pixel is a light blocking pixel that is light-blocked and thereby outputs a pixel signal independent of incident light.
In an imaging device, an electrical charge occurs even when light does not strike a sensor unit at all due to some residual interface state. A current caused by the electrical charge is called a dark current. It is possible to remove noise caused by the dark current by subtracting information obtained by the OB pixel from information obtained by the effective pixel.
On the other hand, to reduce the dark current described above, hydrogen sintering processing may be performed after an uppermost wiring layer is formed. By this hydrogen sintering processing, a dangling-bond, which is an uncombined hand, generated in a gate insulating layer or the dike is terminated by hydrogen, and the interface state is lowered.
In this case, the OB pixel is covered by a light blocking member which is the uppermost wiring layer. Therefore, the OB pixel may not be able to obtain the same effect of the hydrogen sintering processing as the effective pixel. Therefore, in the OB pixel, the interface state is difficult to be lowered and a level of the dark current tends to be higher than that in the effective pixel.
A technique that suppresses the level of the dark current in the OB pixel is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2010-16128. In this patent application publication, a hydrogen diffusion preventing film is formed between a hydrogen supply film and a light blocking member in the OB pixel. The hydrogen diffusion preventing film prevents outward diffusion of hydrogen supplied from the hydrogen supply film. Thereby, sufficient hydrogen is supplied to a surface of a photoelectric conversion element of the OB pixel and a gate insulating layer.